JPS639721B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity sensor that detects humidity.

Currently, there are hygrometers that use human hair or horse tail hair to measure the humidity in the air, but these devices are large-scale and difficult to miniaturize. On the other hand, devices using ceramics have been proposed in an attempt to achieve a solid-state structure, and some are being put into practical use, but there are problems with response speed, and it is still a step away from widespread use.

The present invention has been made in view of these points, and will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view showing the concept of the humidity sensor of the present invention, and FIG. 2 is a top view thereof. In these figures, 1 is a glass substrate, and 2 and 2 are glass substrates 1
The counter electrodes are formed by depositing gold to a thickness of 00 to 400 Å. In addition, the above micro space = 3 is 0.1 to 2
Set to a range of mm. 4 is this counter electrode 2,2
The WO ₃ thin film was formed across a microscopic space of 3.
6000-9500Å using vacuum evaporation method with resistance heating
It is coated to a thickness of .

For a sensor with such a configuration, a constant voltage source 5 is connected between both opposing electrodes 2, 2, as shown in FIG.
When a constant voltage is applied to the WO ₃ thin film 4, the WO ₃ thin film 4 is gradually colored blue, and as the blue coloring progresses, the amount of current applied increases, and when the blue coloring is completed, the amount of current also decreases. Saturation is reached.

Regarding the bluing phenomenon of this WO ₃ thin film 4 and the change in the amount of current, SKDeb is a Philosophical
Magazine, 27, 801 (1973).

When the atmospheric humidity of the sensor that has reached this saturation state is changed, the amount of current changes, and by reading the amount of current with the ammeter 6, the atmospheric humidity at that time can be determined.

The present inventors have devised the following idea regarding such a phenomenon. That is, the WO ₃ thin film formed by vapor deposition has an amorphous surface represented by α-WO ₃ .
Since it is made of materials, it is in a state where it easily absorbs humidity in the air. And the amount of water adsorbed on the surface of the WO ₃ thin film depends on the humidity.

On the other hand, protons (H ⁺ ) and electrons can be introduced into α-WO ₃ by applying an electrochemical electric field, and α-WO ₃ has a different crystal structure from α-WO 3.
Changes to HxWO ₃ (tungsten bronze structure). In other words, a pair of proton and electron is considered to be a hydrogen atom. At this time, X corresponds to the amount of H atoms,
Further, this x is determined by the amount of current and time, that is, the amount of charge, and the maximum value of x corresponds to the maximum amount of H atoms dissolved. When H atoms are introduced into the lattice or grain boundaries of α-WO ₃ , they become blue colored centers, and the larger the value of x, the darker the blue color appears. This is called the electrochromism phenomenon caused by the α-WO ₃ thin film.

On the other hand, the introduction of H atoms is the introduction of protons and electrons as described above, and both protons and electrons are conducted in α-HxWO ₃ , and α-HxWO ₃ can be considered as an electron-ion mixed superionic conductor. Electron conductivity is greater than proton conductivity, α−
The electrical conductivity of HxWO ₃ is given by the electronic conductivity, and its value depends on the amount of H atoms acting as donor atoms, x. This means that in α-HxWO ₃ , the electronic conductivity changes depending on the amount of blue color, that is, the amount of H atoms, and x.

Therefore, the use of a WO ₃ thin film as a humidity sensor requires that the electron conduction in α-HxWO ₃ and the chemical potential of hydrogen atoms be determined after the coloring is completed, that is, after the current flowing through the WO ₃ thin film reaches a saturation state. This corresponds to the amount of water adsorbed on the surface of the WO ₃ thin film, that is, the humidity.

Next, specific examples of the present invention will be explained. Counter electrode 2,
2, 300 Å thick gold is placed with an electrode spacing of 30.1 mm, and 7600 Å thick WO ₃ is placed across both electrodes 2, 2.
A thin film 4 formed with a length of 10 mm and a width of 5 mm was used as a sample.

FIG. 3 shows the measurement results with an ammeter 6 when a constant DC voltage 5 of 30 V was applied to this sample. As is clear from this figure, the voltage was about 10 ^-7 A immediately after applying a constant voltage of 5, but it increased as time passed, and the voltage increased to 7 to 8 A.
After a minute, it reaches about 1.6 to 1.7×10 ^-3 A, and is saturated in that state. At this time, as mentioned above, WO ₃
The thin film 4 becomes blue and gradually increases in blue color, but when the current saturates, the blue color phenomenon also becomes saturated and the blue color does not progress. For reference, the atmospheric temperature at this time was 28°C and the humidity was approximately 57%.

Next, when the sample with the current saturated in this way was placed in a desiccator with silica gel inserted, the current began to decrease, as shown by the solid line in Figure 4, and after about 10 minutes it was about 1.6 mA. About 1.0
mA. After 10 minutes, the sample was taken out of the desiccator and returned to an atmosphere of about 57%.
Although some overshoot is seen after a few minutes, it returns to the state of about 1.6 mA before inputting the desiccator. Also, what is shown by the broken line in Figure 4 is the current change when approximately three times as much silica gel was placed in the desiccator as compared to the previous conditions, and the current decreased more rapidly than in the previous case. . Even in this case, when the sample is removed from the desiccator, it returns to its original state.

On the other hand, Figure 5 shows the case where the sample was placed in a high humidity atmosphere, and the current was saturated in the same way as in the case described above in a desiccator in which a shear cloth containing cotton sufficiently soaked with water was inserted. When the current sample is put in, its current starts to increase and reaches 2.4 in about 10 minutes after being put in.
The current increases to about mA, and when the sample is removed from the desiccator at that point, the current returns to its original state after undergoing some undershoot.

In this way, the current flowing through the sample depends on the humidity, and the relationship between the humidity and the apparent conductivity of the WO ₃ thin film 4 is approximately proportional as shown in FIG. 6 at 28°C. Incidentally, the apparent conductivity referred to here is expressed as: current/potential difference x length of WO ₃ thin film/cross-sectional area of WO ₃ thin film.

Therefore, humidity can be detected from this apparent conductivity, and a solid-state humidity sensor can be used.

Finally, FIG. 7 shows a curve diagram comparing the response speed of the humidity sensor according to the present invention with that of a hair hygrometer. This figure shows the case where the humidity decreased from 98% to 52% and the case where it increased from 27% to 52%. In both cases, the solid line is the measured value with the humidity sensor of the present invention, and the broken line is the hair. This is the reading of the hygrometer. The humidity sensor of the present invention can accurately detect humidity after about 2 minutes, whether the humidity is decreasing or increasing, whereas a hair hygrometer takes several times or more time. It is clear that you are doing so.

In the following explanation of the present invention, the conductivity of the WO ₃ thin film 4 is calculated from the current flowing between the opposing electrodes 2, 2, but as shown in FIG. The detection electrodes 7, 7 are provided on the WO ₃ thin film 4, and this detection depends on _the electrodes 7, 7.
The conductivity may also be detected. In such a configuration, unstable factors near the interface between the counter electrodes 2, 2 and the WO ₃ thin film 4 can be ignored, and the WO ₃ is in a stable state.
It is possible to detect the pure conductivity of the thin film 4, and a humidity sensor with higher accuracy can be obtained.

As is clear from the above description, the present invention is based on WO ₃
Since the configuration detects humidity based on the resistance value of the WO ₃ thin film when the current flowing through the thin film 4 is saturated, the hygrometer can be made into a solid state, improving the reliability and vibration resistance of the hygrometer. It has improved characteristics and can be made smaller, so it can be used in sensors for air conditioners, cookers, etc. In addition, its response speed is much faster than that of hair hygrometers or ceramic type ones, and it can be used as a humidity sensor with a wide range of applications.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the humidity sensor of the present invention, Fig. 2 is a top view thereof, Fig. 3 is a curve diagram showing the state of current flowing through the WO ₃ thin film, and Figs. 4 and 5 are respectively shown as a result of changes in humidity. A curve diagram showing the accompanying change in the amount of current,
FIG. 6 is a curve diagram showing the relationship between humidity and apparent conductivity, FIG. 7 is a curve diagram showing the response speed of the hygrometer, and FIG. 8 is a top view showing another embodiment of the humidity sensor of the present invention. 2 is a counter electrode, 4 is a WO ₃ thin film,
are shown respectively.

Claims (1)

[Claims] 1. Opposing electrodes are provided on the surface of an insulating substrate and are opposed to each other with a minute gap between them, and WO ₃ is applied across the gap between the electrodes.
When a constant voltage is applied between the opposing electrodes and the current flowing at that time is saturated, the humidity to which the WO ₃ thin film is exposed is detected from the conductivity of the WO ₃ thin film at that time. A humidity sensor that is characterized by 2. The humidity sensor according to claim 1, wherein the insulating substrate is a glass substrate. 3. The humidity sensor according to claim 1 or 2, wherein the WO ₃ thin film is an amorphous material. 4. The humidity sensor according to claim 1, 2, or 3, wherein the conductivity of the WO ₃ thin film is calculated from the current flowing between the opposing electrodes. 5. Claims 1, 2, or 3, wherein the conductivity of the WO ₃ thin film is detected by a detection electrode provided on the WO ₃ thin film separately from the counter electrode. Humidity sensor as described in section. 6 Claims 1 and 2, characterized in that the counter electrode is a gold electrode with a film thickness of 300 to 400 Å.
3. The humidity sensor according to item 3, item 4, or item 5. 7. Claim 1, characterized in that the minute distance between the opposing electrodes is in the range of 0.1 to 2.0 mm;
The humidity sensor according to item 2, 3, 4, 5, or 6. 8 Claims 1 and 2, characterized in that the WO ₃ thin film has a thickness of 6000 to 9500 Å.
Paragraph 3, Paragraph 4, Paragraph 5, Paragraph 6, or Paragraph 7
Humidity sensor as described in section.